Verreaux’s eagle population threatened by wind farms

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The demand for renewable power is increasing worldwide and electricity generation from wind power is growing rapidly. There are currently 22 operational wind energy facilities in South Africa, with more than 900 turbines, contributing 1.98 GW to the national grid. The Department of Energy has committed to producing 13.23 GW of renewable energy by 2025, a large portion of which is expected to come from wind power. Although wind energy may contribute to a sustainable solution to increasing energy demands, it is not without environmental impacts. Large raptors are susceptible to turbine collisions, and to date, six Verreaux’s eagle mortalities have been recorded in South Africa.

Verreaux’s eagles (Aquila verreauxii) are listed as Vulnerable in Southern Africa due to decreases in range and abundance recorded by the Southern African Bird Atlas Project. Land use change, habitat loss and
– more recently – the development of the wind energy industry, all pose threats to this species.
The research project started with the investigation of the ecology of Verreaux’s eagles in a natural and an agriculturally transformed habitat in South Africa.

Habitat transformation was predicted to reduce availability of its preferred prey species, the rock hyrax, resulting in reduced breeding productivity or increased foraging efforts. Contrary to this prediction, research in the Cederberg and Sandveld regions of the Western Cape found Verreaux’s eagles can in fact diversify their diet in some agriculturally developed areas, and their breeding productivity does not appear to be negatively impacted.

 Verreaux’s eagle

Portrait of a Verreaux’s eagle. Photo: Maans Booysen

However, this study was restricted to relatively low levels of agricultural transformation. Up to 40% habitat loss was the maximum level encountered by eagles in the Sandveld region. To address the growing conflict with wind energy, researchers are now building a predictive mapping tool for Verreaux’s eagles, to enable the placement of turbines in areas that will minimise the risk of collision. The project utilises high-resolution GPS tracking technology to understand flight behaviour, habitat use and the associated risk of wind turbine collisions. Between 2011 and 2017 16 adult Verreaux’s eagles were fitted with high-resolution GPS tags, and literally millions of 3D GPS fixes have been collected.

Researchers are building a predictive mapping tool for Verreaux’s eagles

Data assists in building statistical models that explore how territory holding eagles use the landscape.
This approach provides insight into how factors such as distance from the nest, the local density of eagles and topographical features influence their 3D movements and the potential risk of wind turbine collisions.

The aim is to incorporate these models within a user-friendly, web-based interface for use by the wind energy industry to obtain a collision risk map of any proposed developments early in the planning stage, thereby ensuring wind turbines can be placed in locations that will minimise risk to flying eagles. Most of the tagged eagles have been one of the birds in a pair, in total eight females and eight males, but there is one pair with both birds tagged. Tracking data from both members of the pair will allow researchers to assess whether there is differential collision risk between the sexes, and will give the first quantitative assessment of pair behaviour in this long-term monogamous species.

The first predictive model has already been used to determine collision risk at four proposed wind development sites in the Karoo, and researchers anticipate it will soon be available more readily to inform Environmental Impact Assessments across the country.

This is an exciting step and researchers are looking forward to working with wind energy developers to enable early identification of risky turbine locations for eagles. It will ultimately reduce the possibility of inappropriately placed turbines and reduce unnecessary mortalities of Verreaux’s eagles due to turbine collisions. This will contribute to the long-term sustainability of wind energy development in Southern Africa and minimise the impact on one of the most widespread and vulnerable eagle species on
the continent.

Written by: Megan Murgatroyd, FitzPatrick Institute of African Ornithology, University of Cape Town

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